Pressure compounding device for hydraulic systems



May 20, 1952 J. TESKE PRESSURE COMPOUNDING DEVICE FOR HYDRAULIC SYSTEMS 2 SHEETS-SHEET 1 Filed March 3, 1949 INVEN TOR. m gdflat Mala/9M m x Z,

Y m B 1 3 M 7 4 6 4 m w 1 z 6 1 M I O a ZG#,A %6L 5 5\X-" O 5 5 5 4 44 5 4 u 5 o O .0 O o 4 5 4/ 5 4. 1 w an, 6 6 m 1; m a a a AT TORNEYS May 20, 1952 L. J. TESKE 2,597,404

PRESSURE COMPOUNDING DEVICE FOR HYDRAULIC SYSTEMS Filed March 5, 1949 x 2 SHEETS-SHEET 2 :plg

INVEN TOR.

Bjy 4% ML ATTORNEYS Patented May 20, 1952 UNITED STATES PATENT OFFICE Kpplieation March 3, .1949, Serial No. "79.367

system which requires only a minor part 'of the foot pedal stroke to move the brake shoes into contact with the brake drums, leaving the larger part of the pedal'stroke for the application of the full braking force.

Another object is to provide a pressure compounding device for a hydraulic braking system of such construction and operating'chara'cteristics that there is substantially no lag in operation during the change over from the application of low pressure to bring the brake shoes into contact with the drumsand the anplication of high pressure to give the full braking force.

It is also an object of the invention to provide such a pressure compounding device which is composed of a relatively small number of parts of simple construction, which can-be installed directly in a standard hydraulic braking system between the master cylinder and the brake cyum ders, and which does not require outside power for operation.

Other objects and advantages of the inven-- tion will be apparent from: the following de-" scription, the accompanying drawing and theap pended claims.

In the drawing Fig. 1 is a diagrammatic view illustrating a hydraulic braking system incorporating a pres-- surecompounding device in accordance with the invention;

Fig. 2 is a view in longitudinal section through the pressure compounding device and showing therelative positions of the parts when the brake is released:

Fig. 3 is a view similar to Fig. 2' showing the relative positions of the parts during the ap=- plication of low braking pressure;

Fig. 4 is a similar view showing the relativepositionsof the parts during the application of the full braking pressure;

Fig. 5 is a View in verticalsection throughthe 8 Claims. (01. -545) pressure relief valve and showing the relative positions of theparts therein whe'n the other parts of the device are-in the positions shown in Figs. 2 and 3; I I

Fig. 6 is a View similar to Fig. 5 showing the relative positions-of the valve parts during the application of full braking pressure;

Fig. 7 is a view in longitudinal section through a modified construction of pressure compounding device;

Fig. 8 is an enlarged section on the line 8 -8 of Fig. 7 and also 'ofFig. 9'; Y

Fig. 9 is arr-enlarged view of a fragment of Fig. '7; and

Fig. 10 is an enlarged section on the line I ll-l it of Fig. 7.

In the drawings, which illustrate preferred embodiments of the present invention, Fig. 1 shows a hydraulic braking system for a motor vehicle wherein a foot pedal II] is operatively connected through a piston rod I l with a piston in a master cylinder l2 having a reservoir l3 for pressurefluid, the pedal I0 being shown as provided with a spring I4 for returningit' to the brake releasing position. The 'pressure'com pounding device ofthe invention is indicated generally at I5, and it is connected at one end by a tube l6 with the'master cylinder'to receive pressure fluid therefrom in response to movement of pedal l0. The-opposite end of the pres sure device I5 is connected bya conduit I! with a coupling I8 from which branch conduits l9 lead to the brake cylinders 20 of the four bralges 2|, which are shown as provided with brake shoes 22, brake drums 23 and-return springs 24 -for shoes 22. A pressure'relief valve 25 ismounted on the pressure device l5 and is shown as connected by a line 26 with the reservoir l3 for the master cylinder.

The internal construction of'the pressure compounding device I5 is shownin detail in Figs. 2 to 6. It includes a cylindrical housing formed to provide two" coaii-ial cylinders 39 and 3| of different cross' sectional areas. The larger cylinder 30 is provided with anend cap 32, and the tube [6 from the master cylinder is connected with the interior of cylinder 30 by means of a-fitting 33 screwed-through cap 32. The smaller cylinder 3| is connected at its outer end to the conduit IT by a fitting 35, and cylinder 30 is provided with a :bleedingplug 36. Cylinder 3| is shown as having'a plug'3'l m the outer end thereof to provide access for' di'sassembly or theunitr I v A pistonlfi is r'eciprocame-washin larger 3 cylinder 30, and it is connected with the smaller piston 4| in cylinder 3| by a common piston rod 42, a screw 43 securing piston 46 to the end of rod 42. The piston 46 thu divides the interior of cylinder 36 into a primary chamber 44, which is adapted to receive pressure fluid from the master cylinder through conduit l6, and a secondary chamber 45 located between the primary chamber and the cylinder 3|. Chamber 45 is sealed from the interior of cylinder 3| by a double acting sealing cup 46 provided with a retaining washer 41 which is press fitted or otherwise secured within the portion of reduced diameter at the inner end of cylinder 30. The piston 4| in cylinder 3| is also provided with a sealing cup 48, which is shown as formed of rubber having a reinforcing washer 49 molded therein and is bolted or otherwise secured to the end of piston 4|.

The larger cylinder 36 is provided with means forming a one-way passage for pressure fluid from the secondary chamber 45 to the primary chamber 44. As shown, the piston 46 is provided with a plurality of bores 56 extending completely therethrough and located adjacent its outer periphery. The piston 46 is also provided with a flexible sealing cup secured thereto by screw 43 within primary chamber 44, and thi cup includes a reinforcing washer 52 of such diameter smaller than that of cylinder 36 that the peripheral lip of cup 5| will flex inwardly away from bores 56 when the pressure within chamber 45 is greater than within chamber 44 to open these bores for the passage of fluid from chamber 45, but the cup will seal bores 56 when the pressure within chamber 44 is greater than that in chamber 45. A sealing cup 53 having a reinforcing insert 54 is also provided at the junction between the outer end of cylinder 36 and the cap 32, and this cup is shown as held in proper position by the fitting 33. A spring 55 is mounted in secondary chamber 45 for returning the piston 46 to its release position following release of the foot pedal.

A vent 56 is provided in cylinder 3| from the space between piston 4| and sealing cup 46, and this vent is connected by a tube 51 with the line 26 to the master cylinder reservoir. In addition, the cylinder 3| is formed with a vent 58 which connects the vent 56 with the interior of cylinder 3| at a position ahead of piston 4| when the latter is in its rest position, and vent 58 thus supplies fluid to cylinder 3| directly from the master cylinder reservoir in accordance with changes in the volume requirements of the brake system as the brakes are adjusted and Without moving piston 4| from its rest position shown in Fig. 2. Piston 4| is also formed with bores 59 similar to the bores 56 in piston 46 which provide passage from vent 56 to the interior of cylinder 3| to the right of piston 4| upon flexing of cup 48.

The pressure relief valve is shown in detail in Figs. 5 and 6. It includes a cylindrical casing 66 provided with a screw fitting 6| threaded into the cylinder 36 and connecting with the secondary chamber 45. A passage 62 through the fitting 6| provides communication from chamber into the interior of casing 66, and inner end of this passage is shown as surrounded by a frusto-conical shoulder or boss 63. A hollow piston 65 is reciprocable within casing 66 and is adapted to seat on the end of boss 63, this end of piston 65 being provided with a passage 66 in line with the passage 62. and surrounded at its outer end by an annular gasket member 6'! for sealing engagement with the end of boss 63. The end of piston 65 opposite passage 66 is closed by a threaded plug 16 having a passage 1| there-' through which is controlled by a ball valve 12 and spring 13. A spring 15 i mounted between the outer end of plug 10 and an adjusting screw 16 threaded in the end cap 11 of casing 66, the spring 15 thus serving normally to urge piston 65 into seated relation with boss 63.

The piston 65 thus divides the interior of casing 66 into two separate valve chambers, the chamber 86 in which the boss 63 is located, and the chamber 8| which receives the spring 15 and which is connected with the master cylinder reservoir |3 by the conduit 26 and fitting 82. These chambers are interconnected by a passage in the wall of casing 66 provided with ports 86 and 81 opening into chambers 86 and 8|, respectively. However, the port 86 is so located as to be closed by the side of piston 65 when the piston is in the seated position hown in Fig. 5.

It will thus be seen that when the piston 65 is in its seated position, the pressure within secondary chamber 45 of cylinder 36 will be transmitted through the passages 62 and 66 and will act on the inner end of plug 16 in opposition to spring 15. and so long as this pressure remains below the predetermined value to which the spring is adjusted, the valve will remain closed. When the pressure in chamber 45 exceeds this predetermined value, it will overcome spring 15 and move piston 65 away from boss 63, thus establishing direct communication from chamber 45 to the master cylinder reservoir through the passages 62 and 85 and the ports 86 and 81, as shown in Fig. 6. It will also be seen that since the annular end surface 88 of piston 65 is of greater effective area than the inner end of plug 16, there is a greater total pressure effective on the piston when the latter is in its open position shown in Fig. 6 than in the closed position, and acordingly a lower pressure in chamber 45 will hold the piston open than is required to effect its initial opening movement.

In operation with this pressure converting device in a hydraulic braking system such as that shown in Fig. 1, the parts are in the relative positions shown in Figs. 2 and 5 when the brakes are released. When the brake pedal is depressed to apply the brakes, it causes a flow of pressure fluid from the master cylinder l2 through the conduit |6 into the primary chamber 44 of cylinder 36, thus causing the pistons 46 and 4| and the piston rod 42 to move from left to right as viewed in the drawing. During this initial movement, the pressure relief valve 25 remains closed, the piston 65 being in its seated position shown in Fig. 5, and accordingly the fluid in chamber 45 will be forced through bores 56 into chamber 44 to equalize the pressures in the two chambers, the sealing cup 5| being forced to flex away from bores 56 as indicated in Fig. 3.

It will also be seen that at this stage of operation, the available volume for additional fluid in chambers 44 and 45 will be increased only to the extent to which the piston rod 42 is displaced from within chamber 45. As a result, since piston rod 42 is of considerably smaller cross-sectional area than the piston 4|, the latter piston will force a correspondingly greater volume of fluid from cylinder 3| into the brake lines l9 than the volume of fluid transferred from the master cylinder to chamber 44 for a given length of stroke of the pistons. The brake shoes 22 will, therefore, be broug t into contact with the brake drums 23 very quickly and after only a minor fraction of the total available stroke'of the foot assert-4.

5 pedal-I0, leaving the major portion of the pedal stroke for the application of the full braking force.

As soon as the shoes are in contact with the drums, the resistance to further movement of pistonM increases to such extent that continued downward movement of the foot pedal'will create a pressure in chambers and 45 in excess of that forwhich the spring I in the pressure relief valve is adjusted, and when this occurs, piston 05 will be unseated to establish direct communication from chamber 45 through the pressure relief valve to the master cylinder reservoir'as already described in connection with Fig. 6. This will in turn effectively open chamber 45 to atmospheric pressure, and the sealing cup 5| will reseat against piston 40 to close bores 50. Thereafter the pressure eiiective on piston 00 from the master cylinder will be directly transferred to piston 4I through piston rod 42 and compounded in accordance with the difierence in cross-sectional areas between these two pistons. Thus during this stage of its operation, the device will act effectively as a hydraulic ram, and th fluid in chamber 45' will offer no resistance to movement of piston 40 except to the extent required to maintain sufficient pressure on valve piston face 08 to hold the valve open.

When the brake pedal is released, the return springs 24 in the brakes will act to return pistons 0| along withpiston 40 and piston rod 42, to the positions shown in Fig. 2, the spring 55 aiding in this return movement. This forces the fluid in chamber 00 back into the master cylinder, and since there is an accompanying pressure drop in chamber 45, the spring 75 will immediately return piston 65 to its seated position closing the pressure'relief valve. Then as the return movement of piston 40 continues, the pressure drop in chamber 45 will create suction effective to unseat the ball valve I2 against its spring and thus to draw fluid back from the master cylinder reservoir through the passage H and through the interior of piston 05 and the passages'fifi and 02 to refill chamber 05.

Figs. 7 to 9 show another construction of pressure compounding device in which a cup-like casting I00 forms a cylinder corresponding to the cylinder 30 in Figs. 2-4, and the interior of this cylinder I00 is shown as connected with the master cylinder by means of a tube I0 and fitting I0 I. The opposite end of cylinder I00 is closed by a plug I02 and annular sealing ring I03. A second casting I05 is secured to cylinder I00 by a threaded connection I00, and this casting includes an inner cylindrical portion IIO which corresponds with the cylinder 3! in Figs. 2 to 4. Casting I05 also includes an annular chamber III which forms a reservoir provided with a vented cap I I2 and connecting with the interior of cylinder IIO through suitable passages H3 and H0. Cylinder IIO accordingly does not require a connection tothe master cylinder reservoir, although such connection ma'y'be provided if desired. Afitting [I5 at the outer' end of easing I05 provides for connecting the interior of cylinder I10 with the conduit I! to the brake cylinders.

A hollow piston rod I20 is mounted for reciprocating movement through the end plug I02 and extends into both of cylinders I00 and H0. Rod I20 includes a piston portion I2I in cylinder I00 which corresponds with the piston 40 and divides the interior of cylinder I00 into a primary chamber I24'and a secondaryfcham'ber I25. Pis- The end of piston rod I20 which is *within cylinder- I I0 carries a hollow piston member I30 enclosing a-chamber I3I Which'is closed 'at' its outer-end by a threaded plug I32 having "an elongated shank or prong I33. A sealing cup I35-is secured to the outer endof thispiston member'I30 toform a piston in cylinder H0 of suitably" smaller effective area than the piston I2 I, for example an area which is -'one-quarterof the area of piston I 2|. It will be noted"that piston I35'divides' the interior of cylinder I00 into a-chamber I40- connecting with the conduit I1 and an annular chamber IOI which'conn'e'cts with the reservoir III through the passagesII3 and II4. It will also be noted that 'a-pa'ssa'ge I42 connects the chamber I3I with chamber MI, and additional passages I44 connect the interior I45 of the hollow piston rod I20 with the secondary chamber I25 in cylinder I00.

A rod I extends through the interiorof the hollow piston rod I20 and carries valves at each end which are arranged to connect the interior I45 of the piston rod alternatelywith the-primary chamber I24 in cylinder I00 and'withthe chamber I3I in the piston member-130. The valve I5I controlsthe connection between the interior of the "piston rod and the chamber I3I, and it includes a cylindrical portion I52 (Fig. 9) having a sliding fit in the outer end of the hollow portion of the piston rod. A coil spring I55 is mounted between'the outer end of 'valve I5I and the plug I32, and this spring is chosento exert "a predetermined force against valve-I5I urging it into a position wherein its washer I55 seats on the annular shoulder I51 in chamber I3I. A fluid portion I58 (Figs. Band 9) of valve I5I, shown as a separate member threaded on rod I50; provides for communication between the interior of the piston rod and the chamber I3I when valve I5I is moved suificiently against spring I55 for its'cylindrical portion I52 to clear the shoulder I51.

The valve I50 at the opposite end of rod- I50 is adapted to seal the connection between the interior of the piston rod I20 and the primary chamber I24 when valve I5I is open. Valve I60 is similar in construction to valve I5I and includes a cylindrical portion I6! having a sliding fit within the enlarged bore I52 in piston I2I -and a fluted portion I63 similar to the-member I58 asjust described. The inner surface'of valve I00 is ground to fit tightly against the'annular shoulder or seat I04 or pinion I2I, and valves I5I and I60 are arranged insuch spaced relation on rod I50 that when one of these valves is in fully seated position, the other is openand vice-versa.

The operation of this formof the invention is similar to that described in connection" with Figs. 2 to '6. When the brakes are released, the pistons I2I and I35 are at their limit of travel for right to left as viewed in Fig. 7, in which position the shoulder I05 on the piston member I30 will be seated against the plug I02. In this position of the parts, there will be no pressure effective in cylinder I00, and the spring I55 will hold valve I-5I in the seated position shown'in Figs. 7 and9. It will also be noted that when piston I35 is in this rest po'sition. the' pas sage-114 will be span-trite chamber -I 40 to simply fluid directly thereto from reservoir III as required during adjustment of the brakes.

In order to assure consistent operation of this device, the relative areas of the pistons, the piston rod I20 and the valves I5I and I60 are correlated with the pressure exerted by spring I55. For example, piston I2I may be four times the area of piston I35, and the latter piston in turn may have twice the area of piston rod I20 in cross section. Similarly the end face I66 of valve I60 should be eight times the area of that portion of valve I5I which is opposed to pressure exerted in piston rod I20 in a direction tending to open valve I5I against spring I55.

When the brake pedal is depressed, fluid is forced from the master cylinder into the primary chamber I24, and this causes movement of the pistons I2I and I35 and the piston rod I20 to the right as viewed in Fig. '7. During this initial movement, until the brake shoes are brought into contact with the drums, fluid will be transferred from secondary chamber I25 into primary chamber I24 through the passages I44 and chamber I45 past the open valve I60. There will also be a temporary transfer of fluid during this stage of operation from reservoir III through the passage II3 into chamber I4I to prevent a negative pressure behind piston I35. Since during this movement the eifective pressure difference on the two sides of piston I2I is equal only to the cross-sectional area of the piston rod I20, it will be seen that with the relative sizes indicated above, the pressure in cylinder I will be twice that in the chamber I40 in cylinder II 0. Thus if, for example, spring I55 is selected to yield and permit valve I5I to open when the pressure in chamber I40 is 100 pounds per square inch, this yielding action will not take place with the relative sizes as stated until the pressure in cylinder I00 reaches 200 pounds per square inch.

When this desired pressure condition is reached and spring I55 is overcome, the rod I50 will be shifted against the spring until valve I60 seats on the end of the piston rod to seal the chamber I45 from primary chamber I24. Since this movement of rod I50 shifts the valve I5I to its open position, the secondary chamber I25 is thus placed in direct connection with reservoir III through the passages I44, the interior I45 of rod I20, the chamber I3I, the passage I42, and the chamber MI and passages II3 and H4. Since the reservoir III is under atmospheric pressure through the vented cap II2, this will relieve the pressure in secondary chamber I25, and thereafter the device will function as a hydraulic ram in essentially the same manner as described in connection with Fig. 4.

When the brake pedal is released, the pistons return to their normal positions under the pressure of the springs in the brake cylinders and the return spring I28. However, since when valve I60 is closed, its exposed surface I66 offers an efiective pressure area which is eight times the effective area of valve I5I against which the pressure could act in initially opening valve I5I against spring I55, the rod I50 will initially remain in its previous position. Thus valve I60 will remain closed and valve I5I open to permit fluid within chamber I4I to return to the secondary chamber I25 through the passages I42 and I44 and the hollow interior I45 of the piston rod.

This condition will continue until the pressure in primary chamber I24 drops to 25 pounds per square inch, at which point the total pressure effective on valve I60 will equal the total pres sure effective on valve I5I when the latter valve initially opened. Spring I55 will accordingly then be effective to shift rod I50 back to the position shown in Fig. 7, thus closing valve I5I and opening valve I60, and during the remainder of the return stroke of the pistons, fluid is supplied from chamber I24 to chamber I25 through the opening at valve I60 and the passages I44. Also, since when the pressure in chamber I24 is 25 pounds per square inch, the effective pressure in chamber I40 is 100 pounds per square inch, it will be seen that the return shifting movement of rod I50 takes place at the same point in the return stroke of the pistons as in their pressure stroke.

Figs. 7 and 10 also illustrate means for assuring operation of the brakes in the event that additional braking force is required after the pistons I2I and I35 have traveled through their full stroke. The fitting II5 encloses a chamber I10 having an opening III (Fig. 10) in the side thereof which receives a fitting I12. A tube I13 leads from the fitting I12 to another fitting I14 in the side of cylinder I00. A sleeve I15 having an internal web I16 and a sealing jacket I11 is slidably mounted within chamber I10, and a spring I normally urges this sleeve from right to left as viewed in Fig.7 to a position wherein it covers and closes the opening I1I.

It will be seen that in the normal operation of this device, the brakes will be fully applied considerably before the pistons and piston rod reach the limit of their stroke, and the pressure fluid will be forced from chamber I40 into conduit I1 through the sleeve I15. However, if this should not occur and ifthe pistons reach the limit of their stroke without applying the desired braking force, the shank or prong I33 will engage web I16 and force sleeve I15 to the right against spring I80, thus opening the connection at I1I into chamber I16. Since piston I2I will by this time have moved past the fitting I14, further movement of the brake pedal will cause fluid to be forced from chamber I24 directly through the tube I13 into the brake lines.

It will accordingly be seen that the present invention provides simple and effective devices for materially increasing the operating efliciency of a hydraulic braking system, and the component parts of these devices are of simple construction promoting economical manufacture and an extended operating life. In operation with one of these devices, the initial movement of the brake shoes into contact with the drums is accomplished by the introduction of a relatively small volume of the pressure fluid from the master cylinder and a correspondingly small fraction of the pedal stroke, leaving the major portion of the stroke for developing the full braking force. In addition, these devices provide for continuous application of the brakes as the pedal is depressed, with no lag during the change over from the initial low pressure application to the high pressure application of braking force, since the shift from low to high pressure is substantially instantaneous simultaneously with the opening of the pressure relief valve.

The invention has the further advantage of providing a self-contained unit which can be readily incorporated in existing hydraulic braking systems without other changes or adjustments to give increased efficiency to the system, and in general a single standard design will fit a wide variety of existing braking systems. It should .7 also=be noted that these .tion primarily on only two simple-relationships the small piston and the piston rod, which establishes. the volume of fluid. required to force the shoes into contact with the drums, and the difference in area between-the two pistons, whiches- -tablishes the pressure available for braking as compared with the effective pressure developed by the master cylinder. The devices can accordingly be readily designed byselection of suitabledimensions for these parts to deliver desired operating characteristics in accordance with the system in which it is to be installed.

While the forms of apparatus herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise forms of apparatus, and' that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

. What is claimed is.

' l. A pressure compounding device adapted for use in a hydraulic braking system including a brake cylinder and a master cylinder, comprising a casing defining a pair of cylinders of different cross-sectional areas, means connecting the larger of said cylinders to said master cylinder to receive pressure fluid therefrom, means connecting the smaller of said cylinders to said brake cylinder to deliver pressure fluid thereto, a large piston operable in said larger cylinder and separating the interior thereof into a primary chamber adapted to receive pressure fluid from said master cylinder and a secondary chamber, a small-piston in said smaller cylinder, a piston rod reciprocable in said casing for connecting said pistons for operation in unison, a reservoir in said casing for pressure fluid, means including a passage in said piston rod connecting said secondary chamber with said reservoir and with said primary chamber, valve means controlling said passage and mounted for shifting movement between a posi tion connecting said secondary chamber with said primary chamber and a position connecting said" secondary chamber with said reservoir, means normally maintaining said valve means in said position connecting said secondary chamber with said primary chamber when the pressure Within said secondary chamber is below a predetermined pressure, and means for shifting said valvemeans to said position connecting said secondary chamber with said reservoir when the pressure in said secondary chamber exceeds said predetermined pressure. 2.. A pressure compounding device adapted for use in a hydraulic braking system including a 'master cylinder and a secondary chamber, a

small piston in said smaller cylinder operable in response to operation of said large piston, pressure relief means operable at a predetermined pressure to relieve the pressure in said secondary chamber, and means forming a valved passage for delivery of pressure fluid from said sec- .ondary chamber to said primary chamber during movement of said large piston in response to the introductionof pressure fluid from said master cylinder into said primary chamber while said pressure relief means is closed, and means operable substantially upon completion of the forward movement of said pistons for directlyconnecting said master cylinder with said brake cylinder to deliver additional pressure fluid thereto.

3. A pressure compounding device adapted for use inra hydraulic system including a brake cylinder and a master cylinder, comprising means forming a pair of coaxial cylinders of diiferent cross-sectional areas, means for connecting the larger of said cylinders to said master cylinder to receive pressure fluid therefrom, means for connecting the smaller of said cylindersv to said brake cylinder to deliver pressure fluid thereto, a large piston operable in said larger cylinder and separating the interior thereof into a primary chamber adapted to receive pressure fluid from said master cylinder and a secondary chamber located between said primary chamber and said smaller cylinders, a small piston in said smaller cylinder, a piston rod connecting said'pistons and extending through said secondary chamber, means forming a valved passage for delivery of pressure fluid from said secondary chamber to said primary chamber during movement of said larger piston in response to the introduction of pressure fluid from said master cylinder into said primary chamber, means operable in response to a predetermined pressure in said secondary chamber to relieve the pressure therein, a passage for'connecting said larger cylinder-directly with said brake cylinder, said-passage being positioned for direct connection with said primary chamber substantially upon completion of. the maximum forward movement of said large piston, a valve in'said smaller cylinder normally closing said passage,-and means onsaid small piston for-opening said valve as said rod approaches the limit of forward movement thereof to eifect direct connection of said brake cylinder with said master cylinder to receive additional pressure fluid therefrom.

4. A pressure compounding device adapted for use in a hydraulic braking system including a brake cylinder and a master cylinder, comprising a casing-defining a pair-of cylinders of different cross-sectional areas, means for connecting the larger ofsaid cylinders to said master cylinder to receive pressure fluid therefrom, means for connecting the smaller of said cylinders tosaid brake cylinder to deliver pressure fluid thereto, a large piston operable in said larger cylinder and Y separating the interior-thereof into a primary chamber adapted to receive pressure fluid from said master cylinder and a secondary chamber, a-small piston in said smaller cylinder, a hollow piston-rod connecting said pistons and extending through said secondary chamber, a reservoir in said casing for pressure fluid, means includingsaid hollow piston rod forming a conand means including said hollow piston rod forming a passageconnecting said secondary chamber and said primary chamber for flow of pressure fluid during'movement of said large piston while said valve means is closed, a-valve for controlling said passage, and a rod reciprocable Within said hollow piston rod carrying both said valve and said valve means for operation in unison when the pressure in said secondary chamber rises above or falls below said predetermined pressure.

5. A pressure compounding device adapted for use in a hydraulic braking system including a master cylinder and a work cylinder, comprising a casing forming a pair of cylinders of different cross-sectional areas, means for connecting the larger of said cylinders to said master cylinder to receive pressure fluid therefrom, means for connecting the smaller of said cylinders to said work cylinder to deliver pressure fluid thereto, a large piston Operable in said larger cylinder and separating the interior thereof into a primary chamber adapted to receive pressure fluid from said master cylinder and a secondary chamber, a small piston in said smaller cylinder operable in response to operation of said large piston, a reservoir in said casing for pressure fluid, a piston rod reciprocable in said casing and connecting said pistons for operation in unison, said small piston being of lesser effective area than said large piston and being of greater effective area than the cross-section of said piston rod, said piston rod being hollow to provide a passage for connecting said primary chamber with said reservoir and having a port therein connecting said passage with said secondary chamber, a rod reciprocable within said passage, a valve on each end of said rod for alternately closing either end of said passage, means nor mally biasing said rod in the direction to close the valve thereon between said passage and said reservoir leaving said secondary chamber connected with said primary chamber, and said rod being shiftable upon overcoming of said biasin means by the pressure in said passage against said closed valve to a position opening said valve to connect said secondary chamber with said reservoir and simultaneously closing the other said valve between said passage and said primary chamber.

6. A pressure compounding device adapted for use in a hydraulic braking system including a master cylinder and a work cylinder, comprising a casing forming a pair of cylinders of different cross-sectional areas, means connecting the larger of said cylinders with said master cylinder, means for connecting the smaller of said cylinders with said work cylinder, a large piston in said larger cylinder separating the interior thereof into a primary chamber connected with said master cylinder and a secondary chamber, a small piston in said smaller cylinder, a reservoir in said casing for pressure fluid, a. piston rod reciprocable in said casing and connecting said pistons for operation in unison, said small piston being of lesser effective area than said large piston and of greater effective area than the cross-section of said piston rod, said piston rod being hollow to provide a passage for connecting said primary chamber with said reservoir and having a port therein connecting said passage with said secondary chamber, a rod reciprocable within said passage, a first valve carried by said rod in said primary chamber for closing the adjacent end of said passage, a second valve at the opposite end of said rod for closing the connection between said passage and said reservoir, means for biasing said rod in the direction to close said second valve leaving said secondary chamber connected with said primary 12 chamber, said rod being shiftable upon overcoming of said biasing means by the pressure in said passage against said second valve to a position opening said second valve to connect said secondary chamber with said reservoir and simultaneously to close said first valve, and the area on said first valve exposed to pressure within said primary chamber in the closed position thereof being substantially greater than the area of said second valve exposed to pressure within said passage in the closed position of said second valve to effect shifting of said rod at the same point in the travel of said piston rod in each direction.

7. A pressure compounding device adapted for use in a hydraulic braking system including a master cylinder and a work cylinder, comprising a casing forming a pair of cylinders of different cross-sectional areas, means connecting the larger of said cylinders with said master cylinder, means connecting the smaller of said cylinders with said work cylinder, a large piston in said larger cylinder separating the interior thereof into a primary chamber connected with said master cylinder and a secondary chamber, a small piston in said smaller cylinder, a reservoir in said casing for pressure fluid, a piston rod reciprocable in said casing and connecting said pistons for operation in unison, said large piston being of greater effective area than said small piston by a predetermined factor, said piston rod being hollow to provide a passage for connecting said primary chamber with said reservoir and having a port therein connecting said passage with said secondary chamber, a rod reciprocable within said passage, a first valve carried by said rod in said primary chamber for closing the adjacent end of said passage, a second valve at the opposite end of said rod for closing the connection between said passage and said reservoir, means for biasing said rod in the direction to close said second valve leaving said secondary chamber connected with said primary chamber, said rod being shiftable upon overcoming of said biasing means by the pressure in said passage against said second valve to a position opening said second valve to connect said secondary chamber with said reservoir and simultaneously to close said first valve, the area of said first valve exposed to pressure within said primary chamber in the closed position thereof being greater by a factor substantially twice as great as said predetermined factor that the area of said second valve exposed to pressure within said passage in the closed position of said second valve.

8. A pressure compounding device adapted for use in a hydraulic braking system including a master cylinder and a work cylinder, comprising a casing forming a pair of cylinders of different cross-sectional areas, means for connecting the larger of said cylinders to said master cylinder to receive pressure fluid therefrom, means for connecting the smaller of said cylinders to said work cylinder to deliver pressure fluid thereto, a large piston operable in said larger cylinder and separating the interior thereof into a primary chamber adapted to receive pressure fluid from said master cylinder and a secondary chamber, a small piston in said smaller cylinder, a reservoir in said casing for pressure fluid, a piston rod reciprocable in said casing and connecting said pistons for operation in unison, said small piston being of lesser effective area than said large piston and being of greater effective area than the Cross-section of said piston rod, said piston rod being hollow to provide a passage for connecting said primary chamber with said reservoir and having a port therein connecting said passage with said secondary chamber, a rod reciprocable within said passage, a valve on each end of said rod for alternately closing either end of said passage, means normally biasing said rod in the direction to close the valve thereon between said passage and said reservoir leaving said secondary chamber connected with said primary chamber, said rod being shiftable upon overcoming of said biasing means by the pressure in said passage against said closed valve to a position opening said valve to connect said secondary chamber with said reservoir and simultaneously closing the other said valve between said passage and said primary chamber, and means operable substantially upon completion of the forward movement of said piston rod for directly connecting said master cylinder with said work cylinder to deliver additional pressure fluid thereto.

LAVERN J. TESKE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 523,419 Thor e July 24, 1894 1,620,115 MacKenzie Mar. 8, 1927 2,001,971 McConkey May 21, 1935 2,031,360 Boughton Feb. 18, 1936 2,166,742 Lambert July 18, 1939 2,374,011 Gunderson Apr. 17, 1945 2,443,642 Rockwell June 22, 1943 

